Ziba, H. ADAMS & A. ADAMS, 1853

GENUS ZIBA H. ADAMS & A. ADAMS, 1853 View in CoL

( FIGS 10F, 14A–D)

Type species: Mitra carinata Swainson, 1824 ; SD, Wenz (1943: 1292).

Diagnosis: Shell small (25–35 mm), elongate to fusiform, usually light brown to olive. Protoconch narrowly conical of about 2.5–3 smooth convex whorls. Suture distinct, impressed. Early teleoconch whorls evenly convex, with weak cancellate sculpture, later whorls typically distinctly carinated. Sculpture of weak grooves on late spire whorls, sometimes missing on last adult whorl. Last adult whorl high, with shell base gradually extended into tapering siphonal canal, typically sculptured with wide and low rounded cords. Siphonal notch weakly or moderately shallow. Aperture elongate, narrow, its outer lip smooth, gently convex or flattened. Inner lip with three fine, oblique columellar folds. Rachidian with five, equally developed, pointed, median cusps, flanked by two notably smaller marginal cusps ( Fig. 10F). Lateral teeth multicuspidate, third proximal cusp strongest, and subsequent cusps gradually diminishing; distal third of tooth smooth, with no cusps.

Distribution: West Africa, continental shelf, on mud.

Species included: Ziba carinata (Swainson, 1824) 1, Z. gambiana (Dohrn, 1861) 3, Z. ogoouensis Biraghi , 19843.

Remarks: The present study has led to a drastic reconsideration of the position and contents of the genus Ziba . Based on the results of our phylogenetic analysis, Ziba is now classified in the subfamily Mitrinae and its contents exclude all the Indo-Pacific and West American species hitherto referred to Ziba by Cernohorsky (1991). An array of Indo-Pacific Ziba species are here transferred to Imbricaria , whereas the Panamic Ziba attenuata is reclassified in Subcancilla , neither of these genera showing an affinity to the true Ziba , which ends up being confined to the tropical eastern Atlantic; to our knowledge, there is no Indo-Pacific species referable to this genus. The radula of Z. carinata shows a plesiomorphic morphology which is commonly found in Mitridae and, although supporting placement of Ziba in Mitrinae , adds little to understanding its relationships within the subfamily. The moderately supported lineage Z. carinata – Episcomitra inferred in the 3-mit tree (though absent in other analyses) may reflect an affinity that makes sense from the biogeographical point of view; however, further studies are needed to determine the relationships of Ziba .